1. Field of the Invention
The present invention relates to zippers and more particularly, to a double layer zipper with tadpole-shaped interlocking teeth that comprises an interlocking series of teeth formed of a left-handed or right-handed series of coils and disposed at each of opposing top and bottom sides of each of two zipper tapes thereof, a seal strip extending along the longitudinal outer side edge of each zipper tape, and a slider equipped with rollers for closing/opening the interlocking series of teeth at the two zipper tapes.
2. Description of the Related Art
A conventional nylon zipper generally comprises two zipper tapes and an interlocking series of teeth at each of the two zipper tapes. Each interlocking series of teeth comprises a left-handed or right-handed series of nylon coils 5. Each nylon coil 5 comprises a coil head 51 and a coil body 52 connected to the front side of the coil head 51. When this nylon zipper tape is closed, the two interlocked series of teeth will not be opened upon a transverse stretching force. However, a potential thief can insert a pointed object, for example, the tip of a ball pen, into a gap between the meshed teeth of the two interlocked series of teeth to separate the two series of teeth. Thus, this structure of nylon zipper has a low level of security when used in a bag or case.
China Patent ZL20082008275716 discloses a double layer zipper that eliminates the drawbacks of the aforesaid conventional nylon zipper. This design of double layer zipper has a high level of safety when used in a bag, case or tent. However, this design of double layer zipper still has room for improvement. For example, it cannot prohibit permeation of external water or moisture.